The development of nano-structured printed electrochemical (bio)sensors for synergic approaches to environmental monitoring

The necessity to monitor the presence of toxic chemicals in the environment has become increasingly urgent during the last century. For this purpose, the emerging development of ad hoc designed electrochemical sensors for the selective and sensitive pollutants detection has attracted growing interest within the researchers’ attention. Indeed, it has been widely reported how the employment of electrochemical sensors allows for a reduction of the costs and the time required for the analysis with conventional techniques, as well as minimising the waste of reagents, resulting in a more environmentally-friendly approach. Basing on these features, electrochemical sensors play a noteworthy role within the scenario of environmental concerns, being particularly suitable for the planning of innovative and sustainable analytical monitoring programmes. Within the research work of my PhD studies, miniaturised electrochemical screen-printed sensors were developed, characterised and applied for the detection of two main categories of highly toxic and polluting chemicals: heavy metals and chemical warfare agents, which represent ones among the most worrying long-term threats for the environment and livings, because of their severe toxicity and persistence in the environment. In order to tune the analytical performances of the herein developed sensors toward the detection of such substances, different nano-structured materials as well as different supports have been employed and combined with the versatile and cost-effective mass production of electrodes by using serigraphic and inkjet printing technologies. The overall approach of this research was focused on the development of synergic strategies to face environmental concerns. In detail, bismuth-based and Nafion-modified sensors, realised onto a flexible and transparent polyester support, were employed for the voltammetric detection of cadmium and lead ions in water samples, as a more affordable and environmentally-friendly alternative to the conventional mercury based sensors. The electrochemical and analytical performances of these sensors upon storage and working conditions were evaluated, in order to improve the reliability of the heavy metal detection. In addition, such sensors were applied for the monitoring of heavy metal content in water environment, as well as biotic tissues, within remediation experiments carried out with filter-feeding organisms. In this way, the heavy metal uptake capability of the organism was examined and characterised, highlighting the high versatility and adaptability of the developed analytical tools for a variety of samples matrices. In a second part of the work, enzymatic inhibition paper-based sensors were realised for the detection of mustard agents, a class of toxic substances used as chemical weapons in the military field as well as in terrorist activities. The use of office and filter paper as support for serigraphic printing, coupled with the use of wax to realise hydrophobic patterns onto the paper sheets, allowed for the development of reagentless and wearable sensing tools for the real-time and on-site detection of this chemical risk. More precisely, the properties of paper were harnessed to integrate the reagents onto the sensor, as well as to allow for easy and safe disposal procedures of the sensors after the detection of these toxic chemicals (i.e. through incineration). The detection of mustard agents were performed by measuring their inhibitory activity toward choline oxidase enzyme, which was assessed through the amperometric measurement of the enzymatic by-product hydrogen peroxide. A Carbon Black/Prussian Blue nanocomposite was employed to enhance the electrochemical performances toward the reduction of hydrogen peroxide. Finally, another approach for the realisation of printed electrodes was investigated, by using inkjet printing technique and paper suitable for the realisation of electronic device as support with the aim to develop miniaturised fully-printed analytical devices, in which all the components, such as electroanalytical sensors, displays, and batteries, are integrated into the same support by printing. In detail, the electrochemical properties of a graphite-based inkjet-printed sensor were characterised by using ascorbic acid as a model analyte, and enhanced by the employment of Carbon Black nanoparticles as electrode modifier. These all-in-one devices pave the way for the improvement of the in-field applicability of printed electrochemical sensors, as well as for the decrease of costs, reagent consumption and waste material production.